Editing HO scale (section)

===Power and control===
[[File:2019 East Texas Model Railroad Club Open House 10 (HO-scale layout).jpg|thumb|East Texas Model Railroad Club HO-scale layout's yard switch controls]]

Model locomotives are fitted with small motors that are wired to pick up power from the rails. As with other scales, HO trains can be controlled in either analog or digital fashions. With analog control, two-rail track is powered by [[direct current]] (varying the [[voltage]] applied to the rails to control [[velocity|speed]], and [[Electrical polarity|polarity]] to control direction). With digital control, such as [[Digital Command Control]] (DCC) or proprietary systems such as the one developed by [[Märklin]], [[Digital data|digital]] commands are encoded at the controller and received by any decoders receiving power from the track. Digital control allows independent control of each locomotive's speed and direction as well as functions not easily achieved with analog control such as reactive sound and lighting effects, integration of auxiliary decoders and automation.

The basic power and control system consists of a power pack of a [[transformer]] and [[rectifier]] (DC), a [[rheostat]]. On large model layouts, the power system may consist of several signal boosters, control interfaces, switch panels and more. Trackage may be divided into electrically isolated sections called blocks and toggle or rotary switches (sometimes relays) are used to select which tracks are energized. Blocking trackage also allows the detection of locomotives within the block through the measurement of current draw.